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Abstract

We report a pitch invariance in cholesteric liquid crystals (CLCs) independent of temperature by mixing two chiral dopants. One dopant tends to shorten the helical pitch of the CLC, but the other makes the pitch longer, with increasing temperatures. From an analysis of temperature dependencies of the pitch for each dopant, we determined the mixing ratio of two chiral dopants for the pitch invariance. Finally, we obtained the pitch-invariant CLCs to temperature and the helical twisting power of the mixed dopant was estimated.

Figures (4)

Concept of a pitch invariance of the CLC independent of temperature. A dopant of S811 tends to shorten a helical pitch but the other S5011 tends to make the pitch longer with increasing temperature. In the mixed dopant with a suitable mixing ratio, the pitch invariance to temperature is obtained.

The reflection spectra of the CLCs doped with (a) S811 (29.97 wt%) and (b) S5011 (2.15 wt%) with increasing temperature, and (c) the corresponding central wavelengths of reflection spectra. The solid lines in (C) depict the least-squares fits to a straight line. The slopes of the red and blue straight lines are fitted to be −4.33 and 2.17, respectively.

The reflection spectra of the CLCs with different concentrations of the mixed dopant (a) 12.98, (b) 15.18, and (c) 18.28 wt% with increasing temperature, and (d) the corresponding central wavelengths of reflection spectra.

The central wavelength as a function of the concentration of the mixed dopant. The solid line depicts the least-squares fit of the measured pitches to Eq. (1) to estimate a HTP of the mixed dopant. The HTP is calculated to be 17.32 ± 1.78 μm−1.